The invention relates generally to a web loading and feeding system including a web and a web handling machine such as a plotter, recorder or sign maker. The web is fed longitudinally of itself through the machine by a pair of sprockets cooperating with holes in two longitudinal side edge portions of the web. The invention deals more particularly with the web for the machine and the pair of sprockets within the machine, the web having a hole arrangement and the sprockets having a pin arrangement which together indicate the proper loading orientation of the web on the sprockets.
Sprockets in machines of the type with which this invention is concerned are typically mounted for rotation about a common drive axis and have pins or teeth-like members on their peripheries which engage rows of holes in two side edge portions of a web being fed. To ensure error free operation, it is important that the web is properly loaded on the machine so that the sprocket pins engage the correct web holes. This means that two corresponding pins of the two sprockets located in a common plane passing through the sprocket drive axis engage two corresponding holes in the web located on a common line extending perpendicular to the longitudinal side edges of the web. When the web is very wide, it is difficult to visually determine which sprocket pins correspond with one another and which holes on the opposite sides of the web correspond with one another and, as a result, web loading errors may occur. The resultant errors in pattern cutting or plotting may be small depending on the degree of misalignment, so the error may go undetected for a considerable period of time, wasting much web material and human labor.
Patent application Ser. No. 529,960 by Logan filed Sept. 6, 1983 and now U.S. Pat. No. 4,834,276, and corresponding South African Patent No. 84/1909 issued on 9-26-84 disclose a web loading and feeding system which provides means to identify the proper loading orientation of a web on a pair of drive sprockets. As disclosed there in reference to one embodiment of that invention, each of the sprockets has a series of radially, outwardly extending driving pins uniformly spaced around the sprocket's periphery and an extra keying pin situated between two of the driving pins. The keying pins of the two sprockets are located in a common plane passing through the axis of the sprockets. An associated web has a longitudinal row of uniformly spaced driving holes in each side edge portion, the spacing of the driving holes corresponds to the spacing of the driving pins. In addition to the driving holes, the web has a longitudinal row of keying holes in each side edge portion, the keying holes in one side edge portion laterally align with the keying holes in the other side edge portion. Also, the spacing of the keying holes in each row corresponds to the size of the sprocket and the location of the keying pins so that the web may be correctly loaded on the sprockets by placing a pair of laterally aligned keying holes over the keying pins of the sprockets.
In the No. 529,960 embodiment described above, the keying pins and the driving pins on both sprockets have the same shape, and the keying pin on each sprocket is somewhat spaced from the closest driving pin. Also, in that embodiment, the keying holes in each side edge portion have the same shape as the driving holes and each keying hole is spaced from the nearest driving hole by a distance corresponding to that between the keying pin and the closest driving pin.
Such a web loading and feeding system has proven effective in minimizing web loading errors of the foregoing type; however, it is desirable to further improve the ease at which and the assurance with which the proper web loading orientation may be visually determined.
Accordingly, a general aim of the invention is to provide a web loading and feeding system comprising a web having a hole arrangement and sprockets having a pin arrangement which web and sprockets readily enable a machine operator to visually determine which holes of the web to place over which pins on the sprockets to properly load the web.
A more specific aim of the invention is to provide a web of the foregoing type having a hole arrangement which wastes little of the web material.
Other aims and advantages of the invention will become apparent from the following detailed description of the preferred embodiments and from the accompanying drawings.